1. Field of the Invention
The present invention is directed to an arrangement for generating a security imprint employing a security module as well as to a method for generating a security imprint, particularly a postal security module is a part of an arrangement that is particularly suited for employment in a postage meter machine or, respectively, mail processing machine or computer with a mail processing capability. The serves for protection against the use of unpaid frankings on postal matter.
2. Description of the Prior Art
European Application 862 143 discloses a postage meter machine for generating and checking a security imprint. A security imprint has a machine-readable marking with variable data and a crypto code or authentification code.
For checking the security imprint, the crypto code or authentification code formed of the variable data is compared to the printed crypto code or authentification code. The postage meter machine has a single microprocessor that calculates a crypto code or a DAC (data authentification code) for securing the print data as well as the print image itself. The latter is composed of fixed frame pixel data and window pixel data. Window pixel data are variable and semi-variable print data.
In order to optimally utilize the calculating time, it has been proposed to insert the print data for the crypto code or a DAC and those variable data that change relatively often into the calculated print image only shortly before the printing. In postage meter machines with column-by-column printing onto moving postal matter, the print line in the print head is orthogonal to the transport direction of the letter. This allows the possibility of transmitting the variable data directly into the print register of the print controller for the print head, with the transmission ensuing sequentially with the frame pixel data. This allows DAC print data that were completely calculated late also to be subsequently embedded during printing. Given run length encoding of the print data, for example, the T1000 postage meter machine of Francotyp-Postalia AG & Co., which employs a thermal transfer printing method, with the prerequisite that some of the fixed frame pixel data and some of the previously embedded window pixel data have already been printed, the DAC print data can be embedded later because the corresponding window must be printed later. If, however, a mail carrier has the requirement that the appertaining window be printed first, the embedding of the print data must ensue in advance. If the changes extend over a number of print columns, whereby more than half of the print columns of the overall print image must be modified, a corresponding lengthening of the calculating time results. A recalculation of the print image with other variable window data and with new DAC print data, however, is then required before every franking image printout. The franking throughput thus is significantly reduced when such print images for a security imprint occur.